As the Colorado River shrinks, there’s a lot on the line: water that supplies 40 million people throughout the southwest, plus farms, wildlife, and hydropower at the nation’s largest reservoirs. The federal agency that deals the most with the Colorado River is the U.S. Bureau of Reclamation. David Arend is the new deputy regional director for the lower basin. He’s worked for the agency for 20 years, most recently overseeing hydropower. He spoke with Alex Hager about some of the biggest issues going forward.